Relay node to control communication resources and relay communication between base station and user equipment

ABSTRACT

A relay node in a mobile communication network for relaying communications between a base station and a mobile terminal. The relay node includes a communication interface that receives resource allocation information from the base station, the resource allocation information indicating a controllable range of communication resources available to the relay node. The relay node also includes a control unit that controls allocation of resources for communication between the relay node and the mobile station based on the received resource allocation information. The relay node then communicates with the mobile terminal based on the control performed by the control unit.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. patent applicationSer. No. 13/394,824 filed on Mar. 8, 2012 which is a U.S. National PhaseEntry Application of the International Patent Appl. No.PCT/JP2010/004763 filed on Jul. 27, 2010 based on Japanese Patent Appl.No. 2010-040224 filed in the Japanese Patent Office on Feb. 25, 2010 andthe Japanese Patent Application No. 2009-220485 filed in the JapanesePatent Office on Sep. 25, 2009.

TECHNICAL FIELD

The present invention relates to a communication system, a base station,a relay node and a user equipment.

BACKGROUND ART

A relay technique is standardized in IEEE (Institute of Electrical andElectronics Engineers) 802.16j. Further, in 3GPP (3rd GenerationPartnership Project) LTE-A (Long Term Evolution-Advanced) also, atechnique using a relay node (RN) is studied actively in order toimprove the throughput of a user equipment (UE) located at the celledge.

The relay node receives a signal transmitted from a base station,amplifies the signal and transmits the amplified signal to the userequipment in the downlink. Such a relay in the relay node ensures ahigher signal-to-noise ratio compared to directly transmitting a signalfrom the base station to the user equipment. Likewise, the relay noderelays a signal transmitted from the user equipment to the base stationin the uplink, thereby maintaining a high signal-to-noise ratio. Therelay node is disclosed in the following non-patent literatures 1 to 3,for example.

CITATION LIST Non Patent Literature

-   [NPL 1] R1-090015, “Consideration on Relay.ppt”, China Potevio,    CATT, January 2009-   [NPL 2] R1-090065, “Joint analog network coding and Relay”,    Alcatel-Lucent, January 2009-   [NPL 3] R1-091803, “Understanding on Type 1 and Type 2 Relay”,    Huawei, May 2009

SUMMARY OF INVENTION Technical Problem

A control range allowed to the relay node (e.g. a variation of a controlmethod for avoiding interference which is allowed to a relay node) isfixed as a possible example. However, because the communication statusof each cell is in flux, it is desired to make the control range of therelay node adaptable to the communication status.

In light of the foregoing, it is desirable to provide a communicationsystem, a base station, a relay node and a user equipment, which arenovel and improved, and which enable an adaptive selection of a controlrange of a small-to-medium-sized base station such as a relay node froma plurality of types of control ranges.

Solution to Problem

In one exemplary embodiment, the present specification discloses a relaynode in a mobile communication network for relaying communicationsbetween a base station and a mobile terminal. The relay node includes acommunication interface that receives resource allocation informationfrom the base station, the resource allocation information indicating acontrollable range of communication resources available to the relaynode. The relay node also includes a control unit that controlsallocation of resources for communication between the relay node and themobile station based on the received resource allocation information.The relay node communicates with the mobile terminal based on thecontrol performed by the control unit.

Advantageous Effects of Invention

According to the embodiments of the present invention described above,it is possible to adaptively select a control range of asmall-to-medium-sized base station such as a relay node from a pluralityof types of control ranges.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an explanatory view showing a configuration of a communicationsystem according to an embodiment of the present invention.

FIG. 2 is an explanatory view showing an example of resource allocationin the case of using the same frequency in UL and DL.

FIG. 3 is an explanatory view showing an example of resource allocationin the case of using different frequencies in UL and DL.

FIG. 4 is an explanatory view showing an example of a format of DL radioframe.

FIG. 5 is an explanatory view showing an example of a format of UL radioframe.

FIG. 6 is an explanatory view showing a connection processing sequence.

FIG. 7 is an explanatory view showing an illustrative example of MBSFNtransmission/reception processing.

FIG. 8 is an explanatory view showing an example of frequency allocationin each cell.

FIG. 9 is a functional block diagram showing a configuration of a userequipment.

FIG. 10 is a functional block diagram showing a configuration of a relaynode.

FIG. 11 is a functional block diagram showing a configuration of a basestation.

FIG. 12 is a functional block diagram showing a configuration of amanagement server.

FIG. 13 is an explanatory view showing the effect of frequency-selectivefading.

FIG. 14 is an explanatory view showing the effect of frequency-selectivefading.

FIG. 15 is an explanatory view showing LTE network architecture.

FIG. 16 is an explanatory view showing a procedure of handover betweenbase stations.

FIG. 17 is a sequence chart showing a connection procedure between auser equipment and a relay node.

FIG. 18 is a sequence chart showing a handover procedure of a relaynode.

FIG. 19 is a sequence chart showing a handover procedure of a userequipment.

FIG. 20 is a sequence chart showing a handover procedure of a userequipment.

FIG. 21 is an explanatory view showing an illustrative example ofdetermination of transmission power.

FIG. 22 is an explanatory view showing an illustrative example ofdetermination of beamforming.

FIG. 23 is an explanatory view showing an illustrative example ofdetermination of transmission timing, insertion of a non-transmissionperiod or the like.

FIG. 24 is an explanatory view showing an illustrative example ofdetermination of transmission timing, insertion of a non-transmissionperiod or the like.

FIG. 25 is an explanatory view showing an illustrative example ofdetermination of transmission timing, insertion of a non-transmissionperiod or the like.

FIG. 26 is an explanatory view showing an illustrative example ofhandover of a relay node.

FIG. 27 is a sequence chart showing an alternative example of aconnection procedure between a user equipment and a relay node.

FIG. 28 is a sequence chart showing a handover procedure of a relaynode.

FIG. 29 is an explanatory view showing an illustrative example ofhandover of a user equipment.

FIG. 30 is a sequence chart showing a handover procedure of a userequipment.

FIG. 31 is a sequence chart showing a handover procedure of a userequipment.

FIG. 32 is an explanatory view showing an example of heterogeneousnetwork architecture.

FIG. 33 is an explanatory view showing an overview of asmall-to-medium-sized base station.

FIG. 34 is an explanatory view showing an interference model in aheterogeneous network.

FIG. 35 is an explanatory view showing an example of interferenceavoidance by handover.

FIG. 36 is an explanatory view showing an example of interferenceavoidance by beamforming.

FIG. 37 is an explanatory view showing an example of interferenceavoidance by transmission power control.

DESCRIPTION OF EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the appended drawings. Note that,in this specification and the appended drawings, structural elementsthat have substantially the same function and structure are denoted withthe same reference numerals, and repeated explanation of thesestructural elements is omitted.

Further, in this specification and the drawings, each of a plurality ofstructural elements having substantially the same function isdistinguished by affixing a different alphabetical letter to the samereference numeral in some cases. For example, a plurality of structuralelements having substantially the same function are distinguished likeuser equipments 20A, 20B and 20C where necessary. However, when there isno particular need to distinguish between a plurality of structuralelements having the same function, they are denoted by the samereference numeral. For example, when there is no particular need todistinguish between the user equipments 20A, 20B and 20C, they arereferred to simply as the user equipment 20.

Preferred embodiments of the present invention will be describedhereinafter in the following order.

1. Basic Configuration of Communication System

(Example of Resource Allocation to Each Link)

(Example of Format of Radio Frame)

(Connection Processing Sequence)

(MBSFN)

(Example of Frequency Allocation to Each Cell)

2. Illustrative Configuration of Communication System

2-1. Configuration of User Equipment

2-2. Configuration of Relay Node

2-3. Configuration of Base Station

3. Control Range A: Central Control of Management Server

4. Control Ranges B and C: Autonomous Control of Relay Node

5. Other Applications of Invention

6. Summary

<1. Basic Configuration of Communication System>

A basic configuration of a communication system 1 according to anembodiment of the present invention is described hereinafter withreference to FIGS. 1 to 8. FIG. 1 is an explanatory view showing aconfiguration of the communication system 1 according to an embodimentof the present invention. Referring to FIG. 1, the communication system1 according to the embodiment of the present invention includes basestations 10A and 10B, a backbone network 12, user equipments 20A, 20Band 20X, and relay nodes 30A and 30B.

The base station 10 manages communication between the relay node 30 andthe user equipment 20 located inside a cell formed by the base station10. For example, the base station 10A manages scheduling information forcommunication with the user equipment 20X located inside the cell, andcommunicates with the user equipment 20X according to the schedulinginformation. Further, the base station 10A manages schedulinginformation for communication with the relay node 30A located inside thecell and scheduling information for communication between the relay node30A and the user equipment 20A.

Note that management of the scheduling information may be performed incooperation by the base station 10 and the relay node 30, may beperformed in cooperation by the base station 10, the relay node 30 andthe user equipment 20, or may be performed by the relay node 30.

The relay node 30 relays communication between the base station 10 andthe user equipment 20 according to the scheduling information managed bythe base station 10. Specifically, the relay node 30 receives a signaltransmitted from the base station 10 and transmits the amplified signalto the user equipment 20 by using frequency/time according to thescheduling information in the downlink. With such a relay in the relaynode 30, a signal-to-noise ratio is higher compared to directlytransmitting a signal from the base station 10 to the user equipment 20near the cell edge.

Likewise, in the uplink also, the relay node 30 relays a signaltransmitted from the user equipment 20 to the base station 10 accordingto the scheduling information managed by the base station 10, therebymaintaining a high signal-to-noise ratio. Although the case where onlythe relay node 30A exists in the cell formed by the base station 10A, aplurality of relay nodes 30 may exist in the cell formed by the basestation 10A.

Proposed as the types of the relay nodes 30 are Type 1 and Type 2. Therelay node 30 of Type 1 has an individual cell ID and is allowed tomanage its own cell. Thus, the relay node 30 of Type 1 operates in sucha way that it is recognized as the base station 10 by the user equipment20. However, the relay node 30 of Type 1 does not completely operateautonomously, and the relay node 30 performs relay communication withinthe range of resources allocated by the base station 10.

On the other hand, the relay node 30 of Type 2, differently from Type 1,does not have an individual cell ID and supports direct communicationbetween the base station 10 and the user equipment 20. For example, arelay transmission technique using cooperative relay or network codingis being studied. The following table 1 shows characteristics of Type 1and Type 2 under study.

TABLE 1 Item Type 1 Type 2 Decision R1-091098 R1-091632 Type of Relay L2and L3 Relay L2 PHY Cell ID Own cell ID No cell ID Transparency Nontransparent Relay Transparent Relay node node to UE to UE New cellCreate new cell (another Not create new cell eNB) RF parametersOptimized parameters N/A HO Inter cell HO HO transparently to UE(generic HO) Control Generate synch. channel, Not generate its ownChannel RS, H-ARQ channel and channel but Generation schedulinginformation decodes/forwards donor etc. eNB's signal to UE BackwardSupport (appear as a Support (able to relay compatibility Rel-8 eNB toRel-8 UE) also to/from Rel-8 UE) LTE-A (Forward Support (it appear —compatibility) differently than Rel-8 eNB to LTE-A UE) Awareness to MS -(>Rel-8 eNB to LTE-A — UEs or Relay) Cooperation Inter cell cooperationIntra cell cooperation Backhaul Higher Lower utilization Usage modelCoverage extension Throughput enhancement and coverage extension CostHigher Lower

The user equipment 20 communicates with the base station 10 directly orthrough the relay node 30 according to the scheduling informationmanaged by the base station 10. Data transmitted or received by the userequipment 20 may be voice data, music data such as music, lectures orradio programs static image data such as photographs, documents,pictures or charts, or video data such as movies, television programs,video programs, game images or the like. Further, the user equipment 20may be an information processing device having a radio communicationfunction such as a mobile phone or a personal computer (PC).

A management server 16 is connected to each base station 10 through thebackbone network 12. The management server 16 functions as a mobilemanagement entity (MME). Further, the management server 16 may functionas a serving gateway. The management server 16 receives managementinformation indicating the status of cell formed by each base station 10from the respective base stations 10 and controls communication in thecell formed by each base station 10 based on the management information.The function of the management server 16 may be incorporated into aplurality of physically separated structures in a distributed manner.

(Example of Resource Allocation to Each Link)

Resource allocation to each link is described hereinafter. In thefollowing description, a communication path between the base station 10and the relay node 30 is referred to as a relay link, a communicationpath between the relay node 30 and the user equipment 20 is referred toas an access link, and a direct communication path between the basestation 10 and the user equipment 20 is referred to as a direct link.Further, a communication path toward the base station 10 is referred toas UL (uplink), and a communication path toward the user equipment 20 isreferred to as DL (downlink). Communication in each link is based onOFDMA.

The relay node 30 separates the relay link and the access link byfrequency or time in order to avoid interference between the relay linkand the access link. For example, the relay node 30 may separate therelay link and the access link in the same direction by TDD (TimeDivision Duplexing) with use of a common frequency.

FIG. 2 is an explanatory view showing an example of resource allocationin the case of using the same frequency in UL and DL. Referring to FIG.2, one radio frame is made up of subframes 0 to 9. Further, in theexample shown in FIG. 2, the relay node 30 recognizes the subframes 8and 9 as resources for DL of the access link according to a directionfrom the base station and therefore relays a signal transmitted from thebase station 10 to the user equipment 20 with use of the subframes 8 and9.

Note that PSC (Primary Synchronization Channel) and SSC (SecondarySynchronization Channel), which are synchronous signals of the downlink,or PBCH (Physical Broadcast CHannel) is allocated to the subframes 0 and5. Further, a paging channel is allocated to the subframes 1 and 6.

FIG. 3 is an explanatory view showing an example of resource allocationin the case of using different frequencies in UL and DL. Referring toFIG. 3, a frequency f0 is used for DL, and a frequency f1 is used forUL. Further, in the example shown in FIG. 3, the relay node 30recognizes the subframes 6 to 8 of the frequency f0 as resources for DLof the access link according to a direction from the base station 10 andtherefore relays a signal transmitted from the base station 10 to theuser equipment 20 with use of the subframes 6 to 8 of the frequency f0.

Note that PSC and SSC, which are synchronous signals of the downlink,are allocated to the subframes 0 and 5 of the frequency f0 (for DL), anda paging channel is allocated to the subframes 4 and 9.

(Example of Format of Radio Frame)

Detailed examples of the frame format of DL radio frame and UL radioframe are described hereinafter with reference to FIGS. 4 and 5.

FIG. 4 is an explanatory view showing an example of the format of DLradio frame. The DL radio frame is made up of subframes 0 to 9, eachsubframe is made up of two 0.5 ms slots, and each 0.5 ms slot is made upof seven OFDM (Orthogonal Frequency Division Multiplexing) symbols.

As shown in FIG. 4, a control channel such as PCFICH (Physical ControlFormat Indicator CHannel), PHICH (Physical Hybrid ARQ Indicator CHannel)or PDCCH (Physical Downlink Control CHannel) is present in the first tothird OFDM symbols at the head of each subframe.

Each of the above channels contains the following information as anexample.

PCFICH: The number of symbols of PDCCH related to Layer 1 and Layer 2

PHICH: ACK/NACK for PUSCH

PDCCH: Downlink control information. Scheduling information (format suchas modulation scheme or coding rate) of PDSCH/PUSCH

Further, one resource block (1RB), which is a minimum unit of resourceallocation, is made up of six or seven OFDM symbols and 12 subcarriers.A demodulation reference (reference signal) is present in a part of theresource block.

Further, SSC, PBCH and PSC are present in the subframes 0 and 5. A freespace in the radio frame shown in FIG. 4 is used as PDSCH (PhysicalDownlink Shared CHannel).

FIG. 5 is an explanatory view showing an example of the format of ULradio frame. Like the DL radio frame, the UL radio frame is made up ofsubframes 0 to 9, each subframe is made up of two 0.5 ms slots, and each0.5 ms slot is made up of seven OFDM symbols.

As shown in FIG. 5, a demodulation reference (reference signal) ispresent in each of the 0.5 ms slots, and a CQI measurement reference ispresent in a distributed manner. The base station 10 or the relay node30 at the receiving end performs channel estimation by using thedemodulation reference and demodulates a received signal according tothe channel estimation result. Further, the base station 10 or the relaynode 30 at the receiving end measures the CQI measurement reference andthereby acquires CQI with the relay node 30 or the user equipment 20 atthe transmitting end.

Further, a free space in the radio frame shown in FIG. 5 is used asPUSCH (Physical Uplink Shared CHannel). Note that, upon receiving arequest for CQI report, the user equipment 20 or the relay node 30transmits the CQI report by using PUSCH.

(Connection Processing Sequence)

A connection processing sequence between the relay node 30 or the userequipment 20 and the base station 10 is described hereinafter withreference to FIG. 6.

FIG. 6 is an explanatory view showing a connection processing sequence.Referring to FIG. 6, the relay node 30 or the user equipment 20transmits RACH (Random Access CHannel) preamble to the base station 10(S62). Receiving the RACH preamble, the base station 10 acquires TA(Timing Advance) information and transmits the TA information togetherwith allocated resource information to the relay node 30 or the userequipment 20 (S64). For example, in the case where the transmissiontiming of the RACH preamble is known, the base station 10 may acquire adifference between the transmission timing and the reception timing ofthe RACH preamble as the TA information.

After that, the relay node 30 or the user equipment 20 transmits RRCconnection request to the base station 10 by using resources indicatedby the allocated resource information (S66). Receiving the RRCconnection request, the base station 10 transmits RRC connectionresolution indicating a transmission source of the RRC connectionrequest (S68). The relay node 30 or the user equipment 20 can therebyconfirm whether the base station 10 has received the RRC connectionrequest.

Then, the base station 10 transmits connection request indicating thatthe relay node 30 or the user equipment 20 is making a request forservice to the management server 16 that functions as MME (S70).Receiving the connection request, the management server 16 transmitsinformation to be set to the relay node 30 or the user equipment 20 asconnection setup (S72).

Then, the base station 10 transmits RRC connection setup to the relaynode 30 or the user equipment 20 based on the connection setup from themanagement server 16 (S74), and the relay node 30 or the user equipment20 makes connection setting. After that, the relay node 30 or the userequipment 20 transmits RRC connection complete indicating completion ofconnection setting to the base station 10 (S76).

Connection between the relay node 30 or the user equipment 20 and thebase station 10 is thereby completed, and communication becomesavailable. The above-described connection processing sequence is just byway of illustration, and the relay node 30 or the user equipment 20 andthe base station 10 may be connected by another sequence.

(MBSFN)

Hereinafter, MBSFN (Multimedia Broadcasting Single Frequency Network)transmission that is performed by the base station 10 and an exemplaryoperation of the relay node 30 in response to the MBSFN transmission aredescribed.

MBSFN is the mode where a plurality of base stations 10 simultaneouslytransmits data in a broadcast manner at the same frequency. Therefore,in MBSFN, the relay node 30 of Type 1 that virtually operates as a basestation transmits a control channel for DL or the like by using the samefrequency as that of the base station 10. A specific flow of MBSFNtransmission/reception processing is described hereinafter withreference to FIG. 7.

FIG. 7 is an explanatory view showing an illustrative example of MBSFNtransmission/reception processing. First, as shown in FIG. 7, the basestation 10 and the relay node 30 simultaneously transmit PDCCH. The basestation 10 transmits, after PDCCH, PDSCH for the user equipment 20 andR-PDCCH for controlling a relay. After R-PDCCH, the base station 10transmits PDSCH for the relay node 30 (relay target data). Anon-transmission period comes after PDSCH for the relay node 30.

The relay node 30 receives, after transmitting PDCCH, PDSCH (relaytarget data) from the base station 10 subsequent to a switching periodto reception processing. The relay node 30 then switches receptionprocessing to transmission processing in the non-transmission periodthat comes after PDSCH (relay target data) from the base station 10.Further, in the next step, the relay node 30 adds PDCCH to decoded PDSCH(relay target data) and then transmits the data to the user equipment20.

The existing user equipment that does not assume the existence of therelay node 30 can thereby make an advantage of the relay by the relaynode 30 without confusion.

(Example of Frequency Allocation to Each Cell)

An example of frequency allocation to each cell in the case where aplurality of cells are adjacent is described hereinafter.

FIG. 8 is an explanatory view showing an example of frequency allocationin each cell. In the case where each cell is made up of three sectors,frequencies f1 to f3 are allocated to the respective sectors as shown inFIG. 8, thereby suppressing the interference of frequencies at the cellboundary. Such allocation is particularly effective in a denselypopulated area with heavy traffic.

In LTE-A, in order to achieve end-to-end high-throughput, various noveltechniques such as spectrum aggregation, network MIMO, uplink multi-userMIMO and relay technique are being studied. Therefore, with the adventof high-throughput novel mobile applications, there is a possibilitythat exhaustion of frequency resources appears as an issue in a suburbanarea also. Further, in the introduction of LTE-A, it is highly possiblethat the installation of the relay node 30 will be activated for thepurpose of achieving infrastructure development at low costs.

<2. Illustrative Configuration of Communication System>

The basic configuration of the communication system 1 according to theembodiment is described above with reference to FIGS. 1 to 8.Hereinafter, an illustrative configuration of the communication system 1according to the embodiment is described with reference to FIGS. 9 to11.

(2-1. Configuration of User Equipment)

FIG. 9 is a functional block diagram showing a configuration of the userequipment 20. Referring to FIG. 9, the user equipment 20 includes aplurality of antennas 220 a to 220 n, an analog processing unit 224, anAD/DA conversion unit 228, and a digital processing unit 230.

Each of the plurality of antennas 220 a to 220 n receives a radio signalfrom the base station 10 or the relay node 30, acquires an electricalhigh-frequency signal, and supplies the high-frequency signal to theanalog processing unit 224. Further, each of the plurality of antennas220 a to 220 n transmits a radio signal to the base station 10 or therelay node 30 based on a high-frequency signal supplied from the analogprocessing unit 224. With the plurality of antennas 220 a to 220 n, theuser equipment 20 is capable of performing MIMO (Multiple-InputMultiple-Output) communication or diversity communication.

The analog processing unit 224 converts the high-frequency signalsupplied from the plurality of antennas 220 a to 220 n into a basebandsignal by performing analog processing such as amplification, filteringand down-conversion. Further, the analog processing unit 224 converts abaseband signal supplied from the AD/DA conversion unit 228 into ahigh-frequency signal.

The AD/DA conversion unit 228 converts the baseband signal supplied fromthe analog processing unit 224 from analog to digital and supplies thedigital signal to the digital processing unit 230. Further, the AD/DAconversion unit 228 converts the baseband signal supplied from thedigital processing unit 230 from digital to analog and supplies theanalog signal to the analog processing unit 224.

The digital processing unit 230 includes a synchronous unit 232, adecoder 234, an encoder 240, and a control unit 242. The synchronousunit 232, the decoder 234, the encoder 240 and so on, together with theplurality of antennas 220 a to 220 n, the analog processing unit 224 andthe AD/DA conversion unit 228, function as a communication unit forcommunicating with the base station 10 or the relay node 30.

A synchronous signal such as PSC or SSC transmitted from the basestation 10 or the relay node 30 is supplied to the synchronous unit 232from the AD/DA conversion unit 228, and the synchronous unit 232performs synchronous processing of the radio frame based on thesynchronous signal. Specifically, the synchronous unit 232 synchronizesthe radio frame by calculating a correlation between the synchronoussignal and a known sequence pattern and detecting a peak of thecorrelation.

The decoder 234 decodes the baseband signal supplied from the AD/DAconversion unit 228 and obtains received data. The decoding may includeMIMO reception processing and OFDM demodulation processing, for example.

The encoder 240 encodes transmission data such as PUSCH and supplies theencoded data to the AD/DA conversion unit 228. The encoding may includeMIMO transmission processing and OFDM modulation processing, forexample.

The control unit 242 controls the overall operation in the userequipment 20, such as transmission processing, reception processing, andconnection processing with the relay node 30 or the base station 10. Forexample, the user equipment 20 performs transmission processing andreception processing by using the resource block allocated by the basestation 10 based on the control of the control unit 242. Note that thecontrol unit 242 controls transmission processing in accordance with atransmission parameter specified by the base station 10 or the relaynode 30. For example, when the base station 10 specifies a TPC (TransmitPower Control) parameter of the user equipment 20 by PDCCH, the controlunit 242 controls transmission processing in accordance with the TPCparameter specified by the base station 10.

Further, when the base station 10 or the relay node 30 makes a requestfor CQI report to the user equipment 20 by PDCCH, the digital processingunit 230 measures channel quality (e.g. reception power) by using thedemodulation reference transmitted from the base station 10 or the relaynode 30. The control unit 242 generates CQI report based on themeasurement result and supplies the generated CQI report to the encoder240. Consequently, the CQI report is transmitted to the base station 10or the relay node 30 by using PUSCH.

(2-2. Configuration of Relay Node)

A configuration of the relay node 30 is described hereinafter withreference to FIG. 10.

FIG. 10 is a functional block diagram showing a configuration of therelay node 30. Referring to FIG. 10, the relay node 30 includes aplurality of antennas 320 a to 320 n, an analog processing unit 324, anAD/DA conversion unit 328, and a digital processing unit 330.

Each of the plurality of antennas 320 a to 320 n receives a radio signalfrom the base station 10 or the user equipment 20, acquires anelectrical high-frequency signal, and supplies the high-frequency signalto the analog processing unit 324. Further, each of the plurality ofantennas 320 a to 320 n transmits a radio signal to the base station 10or the user equipment 20 based on a high-frequency signal supplied fromthe analog processing unit 324. With the plurality of antennas 320 a to320 n, the relay node 30 is capable of performing MIMO communication ordiversity communication.

The analog processing unit 324 converts the high-frequency signalsupplied from the plurality of antennas 320 a to 320 n into a basebandsignal by performing analog processing such as amplification, filteringand down-conversion. Further, the analog processing unit 324 converts abaseband signal supplied from the AD/DA conversion unit 328 into ahigh-frequency signal.

The AD/DA conversion unit 328 converts the baseband signal supplied fromthe analog processing unit 324 from analog to digital and supplies thedigital signal to the digital processing unit 330. Further, the AD/DAconversion unit 328 converts the baseband signal supplied from thedigital processing unit 330 from digital to analog and supplies theanalog signal to the analog processing unit 324.

The digital processing unit 330 includes a synchronous unit 332, adecoder 334, a buffer 338, an encoder 340, and a control unit 342. Thesynchronous unit 332, the decoder 334, the encoder 340 and so on,together with the plurality of antennas 320 a to 320 n, the analogprocessing unit 324 and the AD/DA conversion unit 328, function as areceiving unit, a transmitting unit, and a relay unit for communicatingwith the base station 10 or the user equipment 20.

A synchronous signal transmitted from the base station 10 is supplied tothe synchronous unit 332 from the AD/DA conversion unit 328, and thesynchronous unit 332 performs synchronous processing of the radio framebased on the synchronous signal. Specifically, the synchronous unit 332synchronizes the radio frame by calculating a correlation between thesynchronous signal and a known sequence pattern and detecting a peak ofthe correlation.

The decoder 334 decodes the baseband signal supplied from the AD/DAconversion unit 328 and obtains relay data with a destination to thebase station 10 or the user equipment 20. The decoding may include MIMOreception processing, OFDM demodulation processing, error correctionprocessing and so on, for example.

The buffer 338 temporarily stores relay data with a destination to thebase station 10 or the user equipment 20 which is obtained by thedecoder 334. Then, by the control of the control unit 342, the relaydata with a destination to the user equipment 20 is read from the buffer338 to the encoder 340 in the resource block for DL of the access link.Likewise, by the control of the control unit 342, the relay data with adestination to the base station 10 is read from the buffer 338 to theencoder 340 in the resource block for UL of the relay link.

The encoder 340 encodes the relay data supplied from the buffer 338 andsupplies the encoded data to the AD/DA conversion unit 328. The encodingmay include MIMO transmission processing and OFDM modulation processing,for example.

The control unit 342 controls the overall operation in the relay node30, such as transmission processing, reception processing, andconnection processing with the base station 10 or the user equipment 20.For example, the relay node 30 performs transmission processing andreception processing by using the resource block allocated by the basestation 10 based on the control of the control unit 342.

The controllable range of the control unit 342 is selected by the basestation 10. Specifically, the base station 10 selects one from controlranges A to C, and the control unit 342 controls communication inconformity with the control range selected by the base station 10. Aselection criterion of the control range by the base station 10 anddetails of the control ranges A to C are described later. Although thecase where the base station 10 selects the control range of the controlunit 342 is particularly described in this specification, the selectionof the control range of the control unit 342 may be performed by themanagement server 16.

(2-3. Configuration of Base Station)

FIG. 11 is a functional block diagram showing a configuration of thebase station 10. Referring to FIG. 11, the base station 10 includes aplurality of antennas 120 a to 120 n, an analog processing unit 124, anAD/DA conversion unit 128, a digital processing unit 130, and a backbonecommunication unit 146.

Each of the plurality of antennas 120 a to 120 n receives a radio signalfrom the relay node 30 or the user equipment 20, acquires an electricalhigh-frequency signal, and supplies the high-frequency signal to theanalog processing unit 124. Further, each of the plurality of antennas120 a to 120 n transmits a radio signal to the relay node 30 or the userequipment 20 based on a high-frequency signal supplied from the analogprocessing unit 124. With the plurality of antennas 120 a to 120 n, thebase station 10 is capable of performing MIMO communication or diversitycommunication.

The analog processing unit 124 converts the high-frequency signalsupplied from the plurality of antennas 120 a to 120 n into a basebandsignal by performing analog processing such as amplification, filteringand down-conversion. Further, the analog processing unit 124 converts abaseband signal supplied from the AD/DA conversion unit 128 into ahigh-frequency signal.

The AD/DA conversion unit 128 converts the baseband signal supplied fromthe analog processing unit 124 from analog to digital and supplies thedigital signal to the digital processing unit 130. Further, the AD/DAconversion unit 128 converts the baseband signal supplied from thedigital processing unit 130 from digital to analog and supplies theanalog signal to the analog processing unit 124.

The digital processing unit 130 includes a decoder 134, an encoder 140,a control unit 142, a storage unit 144, and a control range selectionunit 148. The decoder 134, the encoder 140 and so on, together with theplurality of antennas 120 a to 120 n, the analog processing unit 124 andthe AD/DA conversion unit 128, function as a communication unit forcommunicating with the relay node 30 or the user equipment 20.

The decoder 134 decodes the baseband signal supplied from the AD/DAconversion unit 128 and obtains received data. The decoding may includeMIMO reception processing, OFDM demodulation processing, errorcorrection processing and so on, for example.

The encoder 140 encodes PDSCH, for example, and supplies the encodedPDSCH to the AD/DA conversion unit 128. The encoding may include MIMOtransmission processing and OFDM modulation processing, for example.

The control unit 142 controls the overall communication in the cellformed by the base station 10, such as transmission processing,reception processing, connection processing with the relay node 30 orthe user equipment 20, and management of scheduling information. Forexample, the control unit 142 makes scheduling of relay linkcommunication between the base station 10 and the relay node 30 andaccess link communication between the relay node 30 and the userequipment 20.

Further, the control unit 142 stores management information indicatingthe status of the cell formed by the base station 10 into the storageunit 144. An example of the management information is as follows.

(1) Information related to the position of each relay node 30 and eachuser equipment 20 belonging to the base station 10

(2) ID, Qos class and scheduling information of each relay node 30 andeach user equipment 20 belonging to the base station 10

(3) Communication quality information (e.g. CQI information, TPCinformation, or both) of each direct link, each relay link and eachaccess link

(4) Allowable interference level (e.g. a difference between necessarySNTR in the Qos base expected to each communication link and actuallyobserved SINR) of each user equipment 20 belonging to the base station10

The information related to the position of the relay node 30 may containposition information acquired by GPS, TA information indicating thedistance between the base station 10 and the relay node 30, orinformation indicating the direction of the relay node 30. The directionof the relay node 30 can be acquired by algorithm estimating the arrivaldirection of a signal transmitted from the relay node 30 or performingdirectional reception. Likewise, the information related to the positionof the user equipment 20 may contain position information acquired byGPS, TA information indicating the distance between the user equipment20 and the relay node 30, or information indicating the direction of theuser equipment 20.

The control range selection unit 148 selects a control range allowed tothe relay node 30 that belongs to the base station 10 from a pluralityof control ranges. For example, the plurality of control ranges includea control range A (first control range), a control range B (secondcontrol range) and a control range C (third control range). Hereinafter,the respective control ranges are briefly described, and a selectioncriterion of the control range is described after that.

The control range A includes control without the need for “addition” ofextra resources by the relay node 30 (e.g. TPC, link adaptation in therange without the need for addition of resources), and does not includecontrol with the need for change or setting of resources. Thus, in thecase where the control range A is selected, a large part of theoperation of the relay node 30 is controlled by the base station 10.

The control range B includes link adaptation in the range with the needfor addition of resources, handover of the relay node 30, and handoverof the user equipment 20 belonging to the relay node 30. Further, thecontrol range C includes flexible resource scheduling to the userequipment 20 within the range of extra resources allocated by the basestation 10 in addition to the control range B. The resource schedulingindicates the operation necessary for creating a link of a newconnection candidate terminal. For example, in the case of the controlrange B, there is a case where the operation of handover request oracceptance is not sufficiently realized with the distributed amount ofresources allocated to the control range B. In this case, measures suchas further allocating extra resources to the handover destination orfurther allocating extra resources to the relay node 30 and changing thecontrol range to the range C, for example, may be taken.

The control range selection unit 148 selects one of the above controlranges A to C in accordance with the traffic volume in the cell formedby the base station 10. For example, the control range selection unit148 may select the control range B when the traffic volume is within apredetermined level, select the control range A when the traffic volumeis higher than the predetermined level, and select the control range Cwhen the traffic volume is lower than the predetermined level.

Specifically, the control range selection unit 148 may select thecontrol range A when the traffic is congested and there are no availableresources, select the control range B when the available resources are30% or less, and select the control range C when the available resourcesare 30% or more.

Note that, when the control range A is selected, the control unit 142allocates the minimum necessary resources to the relay node 30, and itpreferentially allocates the resource of UL in order to deal with ULconnection request from the user equipment 20.

Further, when the control range B is selected, the control unit 142allocates the resources abundantly to the relay node 30. For example, ifthe amount of resources being used by the relay node 30 is “10”, thecontrol unit 142 may set the amount of resources allocated to the relaynode 30 to “15”. The relay node 30 can thereby instantaneously performlink adaptation for which new resources are necessary.

Further, when the control range C is selected, the control unit 142allocates the extra resources to the relay node 30 according to thenumber of user equipments 20 belonging to the relay node 30. Forexample, the control unit 142 may allocate a larger number of extraresources to the relay node 30 to which a larger number of userequipments 20 belong. Specifically, when the amount of extra resourcesis “40”, one user equipment 20 belongs to the relay node 30A, and threeuser equipments 20 belong to the relay node 30B, the control unit 142may set the amount of extra resources allocated to the relay node 30A to“10” and set the amount of extra resources allocated to the relay node30B to “30”. The relay node 30 can thereby autonomously perform resourcescheduling within the range of the allocated resources. In the casewhere access from the user equipment 20 is concentrated on a certainrelay node 30, the control unit 142 may make the handover of the userequipment 20 to the base station 10 or another relay node 30 for loadsharing.

Note that, although the case where the control range selection unit 148selects the control range in accordance with the traffic volume isdescribed above, the selection method is not limited thereto. Forexample, the control range selection unit 148 may select the controlrange dynamically based on one or a combination of various elements suchas the load of the base station 10, power consumption, the number ofuser equipment 20, whether the relay node 30 is temporarily installedfor an outdoor event, or relationship with another base station.

The backbone communication unit 146 communicates with the managementserver 16 through the backbone network 12. For example, the backbonecommunication unit 146 transmits information described in the above (1)to (4) stored in the storage unit 144 to the management server 16. Atthat time, regarding the above (2), the backbone communication unit 146may further transmit reference counter information for detecting adeviation of synchronization between the base station 10 and anotherbase station in consideration of the case where the base station 10 andanother base station operate in an asynchronous manner.

As described above, the relay node 30 performs control in conformitywith the control range selected by the base station 10. Therefore, theoverall operation of the communication system varies with the controlrange of the relay node 30 selected by the base station 10. Thus,interference avoidance operation in the case where the control range Ais selected and in the case where the control range B or the controlrange C is selected is described hereinafter in detail.

<3. Control Range A: Central Control of Management Server>

In the case where the base station 10 selects the control range A,substantially no autonomous operation is allowed to the relay node 30,and thus the management server 16 performs determination about thepresence or absence of interference and direction of interferenceavoidance control. A configuration of the management server 16 isdescribed hereinbelow. The embodiment is based on the followingpremises.

-   -   The relay node 30 uses the direct link and ends the step up to        RRC connection complete with the base station 10 in the same        procedure as the user equipment 20, and sub-cell ID, reference        pattern allocation and so on are already determined.    -   The base station 10 and the relay node 30 belonging thereto are        in synchronization.    -   Grouping information indicating the relay node 30 and the user        equipment 20 belonging to the relay node 30 is supplied in        advance from the base station 10 (the base station 10 determines        the necessity of relay based on CQI report or TA information and        allocates resources for relay when necessary).    -   Ptx_DL>>Ptx_RL and Ptx_AL (Ptx: maximum transmission power, DL:        direct link (direct link between the base station 10 and the        user equipment 20), AL: access link, RL: relay link)    -   measures against interference to the direct link, particularly        the direct link of user equipment (LTE UE) that does not assume        the existence of the relay node 30, are considered to be an        important issue.

FIG. 12 is a functional block diagram showing a configuration of themanagement server 16. Referring to FIG. 12, the management server 16includes a communication unit 160, a storage unit 162, an interferencedetermination unit 164, and a base station management unit 166. Thefunction of the management server 16 may be implemented in one basestation 10 for central control or may be implemented in a plurality ofbase stations 10 for autonomous control.

The communication unit 160 is connected to each base station 10 and hasfunctions of a receiving unit that receives information from each basestation 10 and a transmitting unit that transmits information to eachbase station 10. For example, the communication unit 160 receives themanagement information described in the above (1) to (4) from each basestation 10. The management information received by the communicationunit 160 is stored in the storage unit 162.

The interference determination unit 164 determines whether interferenceoccurs in communication controlled by different base stations 10 byusing a part or the whole of the management information described in theabove (1) to (4). For example, the interference determination unit 164may determine that interference occurs when the distance between therelay node 30 or the user equipment 20 belonging to a certain basestation 10 and the relay node 30 or the user equipment 20 belonging toanother base station 10 is equal to or shorter than a set value.Further, the interference determination unit 164 may determine thatinterference occurs when resources used by each of the pair whosedistance is equal to or shorter than a set value overlap. Alternatively,the interference determination unit 164 may determine the presence orabsence of interference based on information from the adjacent basestation 10 or the adjacent relay node 30 obtained by measurement in theuser equipment 20.

The base station management unit 166 allows the base station 10 which isdetermined by the interference determination unit 164 that nointerference occurs to perform normal autonomous operation until theupdate of scheduling information, the update of the position of the userequipment 20 or the like or until the lapse of a predetermined reportperiod. On the other hand, the base station management unit 166 directsthe base station 10 that controls communication which is determined bythe interference determination unit 164 that interference occurs toperform interference avoidance operation. Interference avoidance controlis control that is likely to avoid interference or control that avoidsinterference under certain conditions. The interference avoidancecontrol is described hereinbelow.

(Interference Avoidance Control)

When there is an available gap in the traffic of one base station 10that controls communication which is determined that interferenceoccurs, and resource scheduling of one base station 10 can be changed,the base station management unit 166 gives a direction to change thescheduling information of one base station 10 as the interferenceavoidance control. Specifically, the base station management unit 166may change the resources allocated to communication determined thatinterference occurs to different resources in the scheduling informationof one base station 10 and transmit the changed scheduling informationto one base station 10. The base station management unit 166 mayalternatively simply give a notification that a change has been made tothe scheduling information. At this point, the base station managementunit 166 changes not only the scheduling information of communicationbetween one base station 10 and the relay node 30 but also thescheduling information of communication between the relay node 30 andthe user equipment 20.

Further, the base station management unit 166 may allocate resources tothe user equipment 20 by avoiding the resource block or the subcarrierwith a large interference component in the user equipment 20. This isdescribed hereinafter together with the overview of OFDMA.

In OFDMA, the adjacent base stations perform communication by usingcarriers of the same center frequency in a densely populated area. Atthis time, for communication with the user equipment located at the celledge where the coverages of a plurality of base stations overlap, theplurality of base stations avoid interference by using subcarriersorthogonal to each other or different time slots to thereby makeeffective use of the limited resources. On the other hand, in an areawhich is not densely populated, different orthogonal subcarriers arefixedly allocated to each base station in advance because there areoften sufficient resources available.

In this manner, in the case where the adjacent base stations manage theadjacent cells by using the subcarriers orthogonal to each other, theout-of-band power overlaps the sub-carries at their edges due to afrequency deviation by various causes (e.g. the effect of Dopplerfrequency etc.), which causes interference. Therefore, frequencyallocation or out-of-band filtering is important.

Alternatively, in the case where the adjacent base stations manage theadjacent cells by allocating time slots, it is important to adjusttransmission timing in such a way that the boundaries of the time slotsare orthogonal to each other (at least, so as to be within the guardinterval (GI) of the head symbol) based on accurate propagation delay tothe user equipment located at the cell edge.

The effect of frequency-selective fading is described hereinafter withreference to FIGS. 13 and 14.

FIGS. 13 and 14 are explanatory views showing the effect offrequency-selective fading. As shown in FIG. 13, in an OFDM modulatedsignal, while the transmission power of the respective subcarries is thesame at the time of transmission, the reception power of the respectivesubcarries is different at the time of reception due to the effect offrequency-selective fading. Further, as shown in FIG. 14, the size ofthe interference component differs in each resource block.

Thus, in the case where the base station management unit 166 canrecognize the size of the interference component in the user equipment20 with respect to each resource block, it is possible to avoidinterference by allocating resources to the user equipment 20 byavoiding the resource block with a large interference component.Further, in the case where the base station management unit 166 canrecognize the size of the interference component with respect to eachsubcarrier, it is possible to avoid interference by avoiding the use ofthe subcarrier with a large interference component in the resource blockor reducing the modulation scheme.

Note that the base station management unit 166 may notify communicationdetermined that interference occurs to one base station 10 and promptone base station 10 to change the scheduling information, withoutchanging the scheduling information by itself.

Further, the base station management unit 166 may direct the handover ofthe relay node 30 or the user equipment 20 belonging to one base station10 that controls communication determined that interference occurs toanother base station 10 or the relay node 30 belonging to another basestation 10 as the interference avoidance control. Note that the basestation management unit 166 may be based on the premise that there areextra resources for accepting the handover in another base station 10 orthe relay node 30 belonging to another base station 10.

For example, when it is determined that interference is avoidable bymaking the handover of the relay node 30 belonging to one base station10 to another base station 10, the base station management unit 166directs one base station 10 to make the handover. At this time, the basestation management unit 166 notifies ID of the handover destination basestation 10, information for connection or the like to the base station10. In response thereto, a series of operations for the handover areperformed. The information for connection may be the relative distancefrom the handover destination base station 10, information indicatingthe resource block or the subcarrier with a large interference componentdescribed above or the like. Hereinafter, a normal handover procedure orthe like is described, and a flow of the handover of the relay node 30according to the embodiment is specifically described after that withreference to FIGS. 15 to 18.

FIG. 15 is an explanatory view showing LTE network architecture.Referring to FIG. 15, an LTE network includes a S-GW (Serving GW) 18that manages user data in addition to the management server 16 thatfunctions as MME and the base stations 10. Handover between the basestations in such network architecture is performed in the procedureshown in FIG. 16.

FIG. 16 is an explanatory view showing a procedure of handover betweenbase stations. Referring to FIG. 16, in the case where the userequipment 20 and the base station 10A are connected, the base station10A transmits context information (Adjacent eNB context information)indicating a target to be measured such as the adjacent base station 10Bto the user equipment 20 (S404). After that, the user equipment 20measures the radio field intensity or the like of signals transmittedfrom the base station 10B or the like according to the contextinformation while communicating with the base station 10A. Then, theuser equipment 20 reports measurement information (measurement report)to the base station 10A at given intervals or under a given rule (S408).The steps S404 and S408 may be omitted in the case where the basestation 10A makes the handover of the user equipment 20 by compulsorydecision on the network side.

After that, the base station 10A requests the base station 10B to acceptthe handover of the user equipment 20 (S412), and if the acceptance isgranted by the base station 10B (S416), the base station 10A gives acommand to execute the handover to the user equipment 20 (S420). Then,the user equipment 20 performs connection processing with the basestation 10B and then notifies that it is prepared for the handover tothe base station 10B (S424). In response to the notification, the basestation 10B sends ACK back (S428) and reports that the handover of theuser equipment 20 is made to the base station 10B to the managementserver 16/the S-GW 18 (S432).

Although the case where the network side such as the management server16 or the S-GW 18 makes determination about execution of handover basedon the measurement information measured in the user equipment 20 (thecase where the user equipment 20 cooperates) is described above, atrigger of handover is not limited thereto. For example, handover may bemade based on compulsory decision on the network side such as themanagement server 16 or the S-GW 18. Further, the user equipment 20 maytake the initiative to make handover by selecting the base station 10according to measurement information and performing connectionprocessing. Further, the management server 16 may be physically placedto manage a plurality of base stations 10 (eNB) such as MME or S-GW, orthe management server 16 may be assumed to be included in the basestation 10 and information may be exchanged logically with use of X2 IFbetween a plurality of base stations 10.

In LTE-A, coordinated transmission between base stations called CoMP(Coordinated Multipoint Transmission and Reception) has been studied,and each IF (S11 IF, S1-MME IF, S1-U IF) is enhanced, and it is thuslikely that management is made as if one user equipment 20 belongs to aplurality of base stations 10.

Further, at present, a management method of link management such ashandover in consideration of the existence of the relay node 30 is notspecifically discussed. Thus, in the following description, a flow up toconnection of the relay node 30 is described, and a handover procedureof the relay node 30 is described after that. It is assumed in thefollowing description that the management server 16 has the function ofthe S-GW 18 also.

FIG. 17 is a sequence chart showing a connection procedure between theuser equipment 20 and the relay node 30. Referring to FIG. 17, in thecase where the user equipment 20 and the base station 10A are connected,the base station 10A transmits context information (Adjacent eNB & RNcontext information) indicating a target to be measured such as theadjacent base station or the nearby relay node 30 to the user equipment20 (S454). After that, the user equipment 20 measures the radio fieldintensity or the like of signals transmitted from the relay node 30A orthe like according to the context information while communicating withthe base station 10A. Then, the user equipment 20 reports measurementinformation to the base station 10A at given intervals or under a givenrule (S458).

After that, the base station 10A reports measurement information (Relaylink information report) of the nearby relay node 30 to the managementserver 16 (S462). Note that the base station 10A may also transmitmeasurement information of the adjacent base station. Then, themanagement server 16 transmits confirmation for the measurementinformation to the base station 10A (S466). Further, the managementserver 16 determines information for making a connection from the userequipment 20 to the relay node 30 (e.g. ID of the relay node 30 to beconnected) and transmits the information to the base station 10A (S470).Then, the base station 10A makes a relay request for the target relaynode 30 (the relay node 30A in the example of FIG. 17) based on theinformation received from the management server 16 (S474).

Then, when the relay node 30A transmits confirmation for the relayrequest to the base station 10A (S478), the base station 10A gives acommand for connection with the relay node 30A to the user equipment 20(S482). At this point, the base station 10A may notify ID (sub-cell ID)of the relay node 30A recommended for connection. Connection processingbetween the user equipment 20 and the relay node 30A is therebyperformed, so that the user equipment 20 can communicate with the basestation 10A through the relay node 30A. Note that, in the case ofautonomous operation or distributed operation without the need for themanagement server 16, the steps S462, S466 and S470 may be omitted.Further, although the case where the Adjacent eNB & RN specific contextinformation is transmitted from the relay node 30A is shown in FIG. 17,it may be transmitted directly from the base station 10A to the userequipment 20.

FIG. 18 is a sequence chart showing a handover procedure of the relaynode 30. In the example shown in FIG. 18, the user equipment 20 isconnected to the relay node 30A that belongs to the base station 10A. Inthis case, the relay node 30A transmits context information (AdjacenteNB & RN context information) indicating a target to be measured such asthe adjacent base station or the nearby relay node 30 to the userequipment 20 (S504). After that, the user equipment 20 measures theradio field intensity or the like of signals transmitted from the basestation 10B or the like according to the context information whilecommunicating with the relay node 30A. Then, the user equipment 20reports measurement information to the base station 10A through therelay node 30A (S508, S512).

The measurement information may include interfered subcarrier, resourceblock, center frequency or bandwidth, interference node ID, link ID (IDindicating one of direct link, access link and relay link), interferencelevel with respect to each subcarrier or resource block, or SINR levelor the like.

After that, the base station 10A reports measurement information (Relaylink information report) to the management server 16 (S516), and themanagement server 16 transmits confirmation for the measurementinformation to the base station 10A (S520). Then, if the managementserver 16 determines that communication by the relay node 30A interfereswith other communication based on the reported measurement informationor other various kinds of information, the management server 16transmits link management information related to interference avoidancecontrol to the base station 10A (S524). The information related tointerference avoidance control may be ID of a relay node that performscommunication interfering with the relay node 30A, use channel, maximumtransmission power, position information, scheduling information or thelike.

The base station 10A requests the base station 10B to accept thehandover of the relay node 30A based on the link management informationrelated to interference avoidance control which is received from themanagement server 16 (S528), and if the acceptance is granted by thebase station 10B (S532), the base station 10A gives a command to executethe handover to the relay node 30A (S536). Then, the relay node 30Aperforms connection processing with the base station 10B (S540) and thennotifies that it is prepared for the handover to the base station 10B(S544). In response to the notification, the base station 10B sends ACKback (S548) and reports that the handover of the relay node 30A is madeto the base station 10B to the management server 16 (S552).

The relay node 30A may be in the state of multilink connection with aconnection to both the base station 10A and the base station 10B. Inthis case, the relay node 30A may switch the relay link to the basestation 10B only during relay communication of the access link of theuser equipment 20. As a result, the user equipment 20 belongs to thebase station 10B, and thus the base station 10B can control theinterference avoidance between user equipments belonging to the basestation 10B which includes the user equipment 20 in a unified manner.

Note that the relay node 30 may generate a signal to the managementserver 16 in compliance with S1-MMEIF or S1-UIF format and transmits thesignal by radio to the base station 10. In this case, the base station10 can make tunneling of the signal received from the relay node 30 tothe management server 16. The connection between the relay node 30 andthe management server 16 thereby becomes equivalent to directconnection, which makes central control by the management server 16 moreefficient. Further, although the case where the Measurement report istransmitted from the user equipment 20 to the relay node 30A in S508 isshown in FIG. 18, the Measurement report may be transmitted directlyfrom the user equipment 20 to the base station 10A. Likewise, althoughthe case where the Measurement report transmitted from the userequipment 20 is transmitted to the base station 10B by the relay node30A is shown in the lower part of FIG. 18, the Measurement report may betransmitted directly from the user equipment 20 to the base station 10B.Further, although the case where the Adjacent eNB & RN specific contextinformation is transmitted from the relay node 30A is shown in FIG. 18,it may be transmitted directly from the base station 10A to the userequipment 20.

Further, as another example of handover, when the management server 16determines that interference is avoidable by making the handover of theuser equipment 20 belonging to the base station 10 to another relay node30 belonging to the same base station 10, the base station managementunit 166 directs the base station 10 to make the handover. At this time,the base station management unit 166 notifies ID of the handoverdestination relay node 30, information for connection or the like to thebase station 10. In response thereto, a series of operations for thehandover are performed. A flow of the handover of the user equipment 20is specifically described hereinafter with reference to FIG. 19.

FIG. 19 is a sequence chart showing a handover procedure of the userequipment 20. In the example shown in FIG. 19, the relay nodes 30A and30X belong to the base station 10A, and the user equipment 20 isconnected to the relay node 30A. The processing in the steps S554 toS570 in FIG. 19 is substantially the same as the processing in the stepsS504 to S520 in FIG. 18, and detailed explanation thereof is thusomitted.

If the management server 16 determines that interference ofcommunication by the user equipment 20 can be solved by making thehandover of the user equipment 20 to the relay node 30X based on themeasurement information received from the base station 10A in S566 orother various kinds of information, the management server 16 gives acommand to execute the handover of the user equipment 20 to the relaynode 30X by link management information (S574).

The base station 10A requests the relay node 30X to accept the handoverof the user equipment 20 based on the link management informationreceived from the management server 16 (S578), and if the acceptance isgranted by the relay node 30X (S582), the base station 10A gives acommand to execute the handover to the user equipment 20 through therelay node 30A (S584, S586). Then, the user equipment 20 performsconnection processing with the relay node 30X (S590) and then notifiesthat it is prepared for the handover to the base station 10A through therelay node 30X (S592, S594). Then, the base station 10A reports that thehandover of the user equipment 20 is made to the relay node 30X to themanagement server 16 (S596). Note that, although the case where theAdjacent eNB & RN specific context information is transmitted from therelay node 30A is shown in FIG. 19, it may be transmitted directly fromthe base station 10A to the user equipment 20. Further, although thecase where the Measurement report is transmitted from the user equipment20 to the relay node 30A in S558 is shown in FIG. 19, the Measurementreport may be transmitted directly from the user equipment 20 to thebase station 10A. Furthermore, the steps S566, S570 and S574 may beomitted. Further, the Relay connection command in S586 may betransmitted directly from the base station 10A to the user equipment 20.Furthermore, although the case where the Measurement report transmittedfrom the user equipment 20 is relayed to the base station 10A by therelay node 30X is shown in FIG. 19, the Measurement report may betransmitted directly from the user equipment 20 to the base station 10A.Further, the Adjacent eNB & RN specific context information may betransmitted not from the relay node 30X but from the base station 10A.

Further, as another example of handover, when it is determined thatinterference is avoidable by making the handover of the user equipment20 belonging to one base station 10 to the relay node 30 belonging toanother base station 10, the base station management unit 166 directsone base station 10 to make the handover. At this time, the base stationmanagement unit 166 notifies ID of the handover destination relay node30, information for connection or the like to the base station 10. Inresponse thereto, a series of operations for the handover are performed.A flow of the handover of the user equipment 20 is specificallydescribed hereinafter with reference to FIG. 20.

FIG. 20 is a sequence chart showing a handover procedure of the userequipment 20. In the example shown in FIG. 20, the relay node 30Abelongs to the base station 10A, the relay node 30B belongs to the basestation 10B, and the user equipment 20 is connected to the relay node30A. The processing in the steps S604 to S620 in FIG. 20 issubstantially the same as the processing in the steps S504 to S520 inFIG. 18, and detailed explanation thereof is thus omitted.

If the management server 16 determines that communication by the userequipment 20 interferes with communication by the relay node 30B basedon the measurement information received from the base station 10A inS616 or other various kinds of information, the management server 16gives a command to execute the handover of the user equipment 20 to therelay node 30B by link management information (S624).

The base station 10A requests the base station 10B to accept thehandover of the user equipment 20 to the relay node 30B based on thelink management information received from the management server 16(S628), and if the acceptance is granted by the base station 10B (S632),the base station 10A sends ACK back (S636).

After that, the base station 10B makes inquiries about whether thehandover is acceptable to the relay node 30B (S640). If the relay node30B can accept the handover (S644), the base station 10B notifies thatthe relay node 30B can accept the handover to the relay node 30A throughthe base station 10A (S648, S652). Thus, the notification is nottransmitted when the traffic of the relay node 30B is congested or whenthere are no extra resources.

Then, when the relay node 30A gives a command for connection with therelay node 30B to the user equipment 20 (S656), the user equipment 20performs connection processing with the relay node 30B (S660) and thennotifies that it is prepared for the handover to the relay node 30B(S664). Then, the relay node 30B transmits the notification to the basestation 10B (S668), and the base station 10B transmits it to the basestation 10A (S672). The base station 10A then reports that the handoverof the user equipment 20 is made to the relay node 30B to the managementserver 16 (S676). Note that, although the case where the Adjacent eNB &RN specific context information is transmitted from the relay node 30Ais shown in FIG. 20, it may be transmitted directly from the basestation 10A to the user equipment 20. Further, although the case wherethe Measurement report is transmitted from the user equipment 20 to therelay node 30A in S608 is shown in FIG. 20, the Measurement report maybe transmitted directly from the user equipment 20 to the base station10A. Furthermore, the Relay connection command in S652 may betransmitted directly from the base station 10A to the user equipment 20.

On the other hand, when the traffic of one base station 10 that controlscommunication which is determined that interference occurs is toocongested to change the scheduling information, the base stationmanagement unit 166 may direct one base station 10 to inhibit the use ofthe relay node 30 that causes the interference as the interferenceavoidance control. For example, when the resources allocated to therelay nodes 30 belonging to the different adjacent base station 10overlap or when the user equipment 20 belonging to the differentadjacent base stations 10 exist between the base stations 10, the use ofthe relay node 30 is inhibited.

Alternatively, when it is determined that interference is avoidable byadjusting a control parameter based on information related to theposition received from each base station 10 or scheduling information,the base station management unit 166 may determine a control parameterof communication controlled by one base station 10 and give a directionto use the determined control parameter as the interference avoidancecontrol. The control parameter may be a parameter related totransmission power, beamforming, transmission timing, change in guardinterval, insertion of a non-transmission period or the like. Given thedirection for the control parameter from the management server 16, thebase station 10 notifies the control parameter to the relay node 30.Then, the relay node 30 performs communication of the relay link and theaccess link according to the control parameter determined by themanagement server 16. An illustrative example of determination of thecontrol parameter is described hereinafter with reference to thedrawings.

FIG. 21 is an explanatory view showing an illustrative example ofdetermination of transmission power. In the example shown in the upperpart of FIG. 21, the relay node 30A belongs to the base station 10A, theuser equipment 20A belongs to the relay node 30A, the relay node 30Bbelongs to the base station 10B, and the user equipment 20B belongs tothe relay node 30B. Further, the user equipment 20B is included not onlyin a radio range 32B of the relay node 30B but also in a radio range 32Aof the relay node 30A. Therefore, the interference determination unit164 of the management server 16 determines that a signal transmittedfrom the relay node 30A to the user equipment 20A and a signaltransmitted from the relay node 30B to the user equipment 20B interferewith each other in the user equipment 20B.

In this case, the base station management unit 166 determines thetransmission power of the signal from the relay node 30A to the userequipment 20A as transmission power capable of avoiding interference.Specifically, as shown in the lower part of FIG. 21, the base stationmanagement unit 166 reduces the transmission power so that the userequipment 20B becomes excluded from the radio range 32A of the signaltransmitted from the relay node 30A to the user equipment 20A. It isthereby possible to avoid the interference caused by the relay node 30A.

FIG. 22 is an explanatory view showing an illustrative example ofdetermination of beamforming. In the example shown in the upper part ofFIG. 22, the relay node 30A belongs to the base station 10A, the userequipment 20A belongs to the relay node 30A, the relay node 30B belongsto the base station 10B, and the user equipment 20B belongs to the relaynode 30B. Further, the user equipment 20B is included not only in theradio range 32B of the relay node 30B but also in the radio range 32A ofthe relay node 30A. Therefore, the interference determination unit 164of the management server 16 determines that a signal transmitted fromthe relay node 30A to the user equipment 20A and a signal transmittedfrom the relay node 30B to the user equipment 20B interfere with eachother in the user equipment 20B.

In this case, the base station management unit 166 determines to performbeamforming in order to prevent the signal transmitted from the relaynode 30A to the user equipment 20A from causing interference.Specifically, as shown in the lower part of FIG. 22, the base stationmanagement unit 166 makes beamforming so that the user equipment 20Bbecomes excluded from the radio range 32A of the signal transmitted fromthe relay node 30A to the user equipment 20A. In this manner, it ispossible to avoid the interference caused by the relay node 30A by wayof beamforming also.

FIGS. 23 to 25 are explanatory views showing illustrative examples ofdetermination of transmission timing, insertion of a non-transmissionperiod or the like. In the example shown in FIG. 23, the user equipment20B is included in the radio range of the base station 10A and the relaynode 30B. Even when the base station 10A and the relay node 30B transmitsignals in temporally orthogonal slots, the time of receipt in the userequipment 20B coincides with each other in some cases as shown in FIG.24. Specifically, FIG. 24 shows the case where the first half of thesignal transmitted from the base station 10A and the latter half of thesignal transmitted from the relay node 30B interfere with each other.

In this case, as shown in FIG. 25, the base station management unit 166may delay the transmission timing of the signal from the base station10A. Alternatively, the base station management unit 166 may set severalOFDM symbols at the head of the signal transmitted from the base station10A as the non-transmission period or lengthen the GI. The base stationmanagement unit 166 may alternatively advance the transmission timing ofthe relay node 30B. In this manner, it is feasible in some cases toavoid interference by adjusting the transmission timing or inserting thenon-transmission period.

As described above, the base station management unit 166 can directexecution of various ways of interference avoidance control. Further,each base station 10 reports the process of execution of interferenceavoidance control or the communication quality information afterexecution to the management server 16, and the base station managementunit 166 adjusts the control parameter as appropriate based on thereported communication quality information. Note that, when a requestfor the communication quality information is made from the managementserver 16, each base station 10 may report the communication qualityinformation to the management server 16 as soon as it is ready.

For example, the base station management unit 166 may give a directionto increase the transmission power by using TPC of the correspondinglink when the number of occurrences of HARQ (Hybrid Automatic RepeatreQuest) reported from the base station 10 is a specified number orgreater or when a packet loss is a predetermined level or higher.

Further, in the layout shown in FIG. 21, if the signal from the relaynode 30B to the base station 10B interferes with the signal from theuser equipment 20A to the relay node 30A, the base station managementunit 166 may give a direction to decrease the rate of the signal fromthe user equipment 20A to the relay node 30A or change the HARQ. Notethat the HARQ scheme may be chase combining, incremental redundancy orthe like.

<4. Control Ranges B and C: Autonomous Control of Relay Node>

In the case where the base station 10 selects the control range B or C,autonomous operation is allowed to the relay node 30, and thus the relaynode 30 autonomously determines interference avoidance control andexecutes the interference avoidance control. The autonomous operation bythe relay node 30 is described hereinbelow.

(Information Supplied from Management Server 16)

The management server 16 supplies the following information to the relaynode 30 determined to cause interference by the interferencedetermination unit 164 through the base station 10.

-   -   Information related to positions of the relay node 30 belonging        to the nearby base station 10 that controls communication        interfering with the relay node 30 and user equipment. It        includes both cases where communication of the relay node 30        gives interference and where it receives interference.    -   ID, Qos information, and scheduling information of the relay        node 30 belonging to the nearby base station 10 that controls        communication interfering with the relay node 30 and user        equipment. It includes reference counter information for        detecting a deviation of synchronization when the relay node 30        and the nearby base station 10 are asynchronous.

The management server 16 may select part of the information related toposition or the scheduling information described above and supplies theselected part. Further, the management server 16 may notify recommendedinterference avoidance control (control parameter etc.) to the relaynode 30.

The relay node 30 determines and executes interference avoidance controlbased on the above information supplied from the management server 16.Handover and link adaptation are examples of the interference avoidancecontrol. The interference avoidance control is described in detailhereinbelow.

(Interference Avoidance Control: Handover)

FIG. 26 is an explanatory view showing an illustrative example ofhandover of the relay node 30. In the example shown in the upper part ofFIG. 26, the relay node 30A belongs to the base station 10A, the userequipment 20A belongs to the relay node 30A, and the user equipment 20Bbelongs to the base station 10B. Note that the relay node 30A mayrecognize the cell configuration shown in the upper part of FIG. 26based on the information related to position which is supplied from themanagement server 16.

In the example shown in the upper part of FIG. 26, if the relay node 30Atransmits a signal to the base station 10A and by the relay link UL and,simultaneously, the user equipment 20B transmits a signal to the basestation 10B by the direct link UL, the both signals can interfere witheach other at the base station 10B. In light of this, the control unit342 of the relay node 30A refers to the scheduling information of thebase station 10B which is supplied from the management server 16, and ifthere are extra resources for accepting handover in the base station10B, it may execute the handover of the relay node 30A to the basestation 10B.

Consequently, as shown in the lower part of FIG. 26, the relay node 30Ais connected to the base station 10B and belongs to the base station10B. If the relay node 30A belongs to the base station 10B, the basestation 10B performs scheduling in such a way that the user equipment20B and the relay node 30A do not interfere with each other, and it isthus possible to avoid the interference of a signal transmitted from therelay node 30A and a signal transmitted from the user equipment 20B.

Note that the relay node 30A may execute handover based on themeasurement information reported from the user equipment 20A.Hereinafter, an alternative example of a connection procedure betweenthe user equipment 20A and the relay node 30A is described, and ahandover procedure is described after that.

FIG. 27 is a sequence chart showing an alternative example of aconnection procedure between the user equipment 20A and the relay node30A. The user equipment 20A transmits RRC connection request to therelay node 30A by using the resources allocated from the relay node 30A(S704). The relay node 30A receives the RRC connection request from theuser equipment 20A and then requests the base station 10A to makeresource allocation for the relay link and the access link (S708). Ifthe base station 10A can make resource allocation requested from therelay node 30A, the base station 10A gives a notification that theallocation can be made and the allocated resources to the relay node 30A(S712).

Then, the relay node 30A transmits ACK to the base station 10A (S716)and then transmits RRC connection resolution indicating a transmissionsource of the RRC connection request (S720). The base station 10A thentransmits Connection request indicating that the user equipment 20A ismaking a request for service to the management server 16 (S724). Themanagement server 16 receives the Connection request and transmitsinformation to be set to the user equipment 20A as Connection setup(S728).

The base station 10A then transfers the Connection setup from themanagement server 16 to the relay node 30A (S732), the relay node 30Atransmits RRC connection setup to the user equipment 20A (S736), and theuser equipment 20A makes connection setting. After that, the userequipment 20A transmits RRC connection complete indicating thatconnection setting is completed to the relay node 30A (S740). The userequipment 20A and the relay node 30A are thereby connected, so that theuser equipment 20A can communicate with the base station 10A through therelay node 30A.

FIG. 28 is a sequence chart showing a handover procedure of the relaynode 30A. In the example shown in FIG. 28, the relay node 30A belongs tothe base station 10A, and the user equipment 20A and the relay node 30Aare connected. In this case, the relay node 30A transmits contextinformation (Adjacent eNB & RN context information) indicating a targetto be measured such as the adjacent base station or the nearby relaynode 30 to the user equipment 20A (S754). After that, the user equipment20A measures the radio field intensity or the like of signalstransmitted from the base station 10B or the like according to thecontext information while communicating with the relay node 30A. Then,the user equipment 20A reports measurement information to the relay node30A (S758).

Then, if the relay node 30A determines that the handover to the basestation 10B is effective for avoiding interference based on themeasurement information received from the user equipment 20A,information from the management server 16 or the like, the relay node30A performs connection processing with the base station 10B (S762).During the connection processing of the relay node 30A, it is difficultfor the relay node 30A to relay communication of the user equipment 20A.Thus, when the relay node 30A has transmission/reception resources (e.g.a plurality of antennas) that enable execution of a plurality of kindsof processing in parallel, the relay node 30A may use some of thetransmission/reception resources for communication with the userequipment 20A and use other transmission/reception resources forconnection processing with the base station 10B. Alternatively, therelay node 30A may make the user equipment 20A directly connected to therelay node 30A and, after the end of connection processing with the basestation 10B, make the user equipment 20A connected back to the relaynode 30A.

After that, the relay node 30A performs measurement based on contextinformation received from the base station 10B and transmits themeasurement information to the base station 10B (S766). Further, therelay node 30A transmits the context information to the user equipment20A and receives the measurement information obtained by measurement inthe user equipment 20A from the user equipment 20A (S770).

On the other hand, interference can be avoided in some cases by thehandover of the user equipment 20, not the relay node 30, as describedbelow.

FIG. 29 is an explanatory view showing an illustrative example of thehandover of the user equipment 20. In the example shown in the upperpart of FIG. 29, the relay node 30A belongs to the base station 10A, theuser equipment 20A belongs to the relay node 30A, and the relay node 30Band the user equipment 20B belong to the base station 10B.

In the example shown in the upper part of FIG. 29, if the relay node 30Atransmits a signal received from the user equipment 20A to the basestation 10A by the relay link UL and, simultaneously, the user equipment20B transmits a signal to the base station 10B by the direct link UL,the both signals can interfere with each other at the base station 10B.In light of this, the control unit 342 of the relay node 30A refers tothe scheduling information of the base station 10B which is suppliedfrom the management server 16, and if there are extra resources foraccepting handover in the base station 10B, the handover of the userequipment 20A may be made to the base station 10B.

Specifically, the relay node 30A may shut down the connection with theuser equipment 20A. This is because the user equipment 20A would attemptto make a connection with the base station 10B after that.Alternatively, the relay node 30A may explicitly request the basestation 10B or the relay node 30B to make the handover of the userequipment 20A.

As shown in the lower part of FIG. 29, if the handover of the userequipment 20A is made to the relay node 30B, the relay node 30A ceasesto relay the signal transmitted from the user equipment 20A, so that itis possible to avoid the interference shown in the upper part of FIG.29. Note that the relay node 30A may control the handover of the userequipment 20 when the number of user equipment 20 belonging to the relaynode 30A is a predetermined number or greater (when the number ofequipment which can be handled is close to the limit). Further, therelay node 30A may select the user equipment 20 where the access linkCQI does not satisfy a given criterion as a target of handover.

The relay node 30A may execute handover based on measurement informationreported from the user equipment 20A. A handover procedure of the userequipment 20A is described hereinafter with reference to FIG. 30.

FIG. 30 is a sequence chart showing a handover procedure of the userequipment 20A. In the example shown in FIG. 30, the relay node 30Abelongs to the base station 10A, the relay node 30B belongs to the basestation 10B, and the user equipment 20A is connected to the relay node30A. In this case, the relay node 30A transmits context informationindicating a target to be measured such as the adjacent base station orthe nearby relay node 30 to the user equipment 20A (S804). After that,the user equipment 20A measures the radio field intensity or the like ofsignals transmitted from the base station 10B, the relay node 30B or thelike according to the context information while communicating with therelay node 30A. Then, the user equipment 20A reports measurementinformation to the relay node 30A (S808).

Then, it is assumed that the relay node 30A determines that the handoverof the user equipment 20A to the relay node 30B is effective foravoiding interference based on the measurement information received fromthe user equipment 20A, information from the management server 16 or thelike. In this case, the relay node 30A makes a request for the handoverof the user equipment 20A to the relay node 30B to the base station 10Bthrough the base station 10A (S812, S816). Then, the base station 10Btransmits confirmation for the handover request to the base station 10A(S820) and receives ACK from the base station 10A (S824).

After that, the base station 10B makes inquiries about whether thehandover is acceptable to the relay node 30B (S828). If the relay node30B can accept the handover of the user equipment 20A (S832), the basestation 10B notifies that the relay node 30B can accept the handover tothe relay node 30A through the base station 10A (S836, S840).

Then, the relay node 30A transmits context information and a signal forrecommending the handover to the relay node 30B (S844, S848). Further,the relay node 30A makes a request for shutdown of the connection withthe relay node 30A to the user equipment 20A (S852), and when the relaynode 30A receives confirmation for the connection shutdown from the userequipment 20A (S856), it sends ACK back to the user equipment 20A(S860). Connection between the user equipment 20A and the relay node 30Ais thereby shut down, and the user equipment 20A performs connectionprocessing with the relay node 30B to which handover is recommended(S864).

Although the case of performing both of recommendation of the handoverto the relay node 30B and request for shutdown of the connection withthe relay node 30A is described above, either one or both of them arenot necessarily performed. For example, the relay node 30A maycompulsorily shut down the connection with the user equipment 20Bwithout performing both of the above processing. In this case, the userequipment 20B is expected to take the initiative to make connectionprocessing with the base station 10 or the relay node 30 included in thecontext information.

Further, although the case where the handover of the user equipment 20Ais made to the relay node 30B belonging to a different base station isdescribed above, the handover may be made to the relay node 30Xbelonging to the same base station 10A as described below.

FIG. 31 is a sequence chart showing a handover procedure of the userequipment 20A. In the example shown in FIG. 31, the relay node 30A andthe relay node 30X belong to the base station 10A, and the userequipment 20A is connected to the relay node 30A. The relay node 30Areceives measurement information from the user equipment 20A (S904) anddetermines interference avoidance control of communication with the userequipment 20A based on the measurement information and informationsupplied from the management server 16 or the like. If the relay node30A determines that the handover of the user equipment 20A to the relaynode 30X is effective for avoiding interference, the relay node 30Atransmits context information and a signal for recommending the handoverto the relay node 30X (S908, S912).

Further, the relay node 30A makes a request for shutdown of theconnection with the relay node 30A to the user equipment 20A (S916), andwhen the relay node 30A receives confirmation for the connectionshutdown from the user equipment 20A (S920), it sends ACK back to theuser equipment 20A (S924). Connection between the user equipment 20A andthe relay node 30A is thereby shut down, and the user equipment 20Aperforms connection processing with the relay node 30X to which handoveris recommended (S928).

As described above, the relay node 30 can avoid interference byexecuting the handover to the adjacent base station 10 or making thehandover of the user equipment 20 belonging to the relay node 30 toanother relay node 30.

(Interference Avoidance Control, Link Adaptation)

If the slot that is likely to cause interference, the relay node 30 withwhich interference occurs, ID of the user equipment 20 or the basestation 10, information related to position and an allowableinterference level are notified from the management server 16, the relaynode 30 can avoid interference by link adaptation in some cases. Thelink adaptation of the access link that is controllable by the relaynode 30 may be TPC, AMC (Advanced Modulation Control), HARQ or the like.Each link adaptation is specifically described hereinbelow.

When the relay node 30 is directed to reduce the interference level onother communication by the management server 16 or the like, or when therelay node 30 determines to reduce the interference level on othercommunication, the relay node 30 executes any of the following linkadaptations:

(1) Reduce transmission power. Further, increase reception SNIR with useof HARQ

(2) Reduce transmission power. Further, reduce necessary SNIR byreducing a modulation and coding rate.

Addition resources are necessary when the relay node 30 executes any ofthe above (1) and (2). Therefore, when extra resources are allocated inadvance from the base station 10, the relay node 30 uses the extraresources, and when there are no sufficient extra resources, the relaynode 30 makes a request for resource allocation to the base station 10or the management server 16. Note that, when the base station 10 or themanagement server 16 receives a request for resource allocation to avoidinterference, they perform resource allocation in preference to otherrequests.

On the other hand, when the relay node 30 performs communication whilethe interference level received from other communication is high, therelay node 30 executes any of the following link adaptations:

(3) Increase transmission power.

(4) Increase reception SNIR with use of HARQ

(5) Reduce necessary SNIR by reducing a modulation and coding rate.

In order to execute the above (4) and (5), additional resources arenecessary. Therefore, when extra resources are allocated in advance fromthe base station 10, the relay node 30 uses the extra resources, andwhen there are no sufficient extra resources, the relay node 30 makes arequest for resource allocation to the base station 10 or the managementserver 16. Note that, when the base station 10 or the management server16 receives a request for resource allocation to avoid interference,they perform resource allocation in preference to other requests.

Further, in OFDMA, the link adaptation can be performed in units ofresource blocks or subcarriers. Thus, the relay node 30 may execute thelink adaptations described in the above (1) to (5) only on thesubcarrier or the resource block where the interference level exceeds apredetermined level. Specifically, when the relay node 30 transmitssignals by using a resource block A where the interference level fromother communication is higher than a predetermined level and a resourceblock B where it is lower than the predetermined level, the relay node30 may execute any one of the above (3) to (5) only on the resourceblock A.

<5. Other Applications of Invention>

In the foregoing, explanation has been given about that a control rangeallowed to the relay node 30 is selected from a plurality of types ofcontrol ranges, that the management server 16 achieves central controlfor avoiding interference between cells formed by the respective basestations 10, and that the relay node 30 autonomously determinesinterference avoidance control and executes the interference avoidancecontrol. However, the above-described relay node 30 is just an exampleof small-to-medium-sized base stations in the heterogeneous networkdescribed below.

Thus, it is also within the scope of the present invention that acontrol range allowed to a small-to-medium-sized base station isselected from a plurality of types of control ranges, that themanagement server 16 achieves central control for avoiding interferencebetween cells formed by the respective base stations 10 orsmall-to-medium-sized base stations, and that a small-to-medium-sizedbase station autonomously determines interference avoidance control andexecutes the interference avoidance control.

A heterogeneous network is a network where a plurality ofsmall-to-medium-sized base stations coexist in a macro cell byperforming overlay transmission or spectrum sharing. Thesmall-to-medium-sized base station may be a RRH (Remote RadioHead) cellbase station, a hotzone base station (Pico/micro cell eNB), a femtocellbase station (Home eNB), a relay node (relay base station) or the like.The heterogeneous network architecture is specifically described below.

FIG. 32 is an explanatory view showing an example of heterogeneousnetwork architecture. Referring to FIG. 32, the heterogeneous networkincludes a macro cell base station 10 (which is synonymous with a basestation 10), a relay node 30, a hotzone base station 31, a femtocellbase station 32, RRH cell base stations 33 and management servers 16Aand 16B.

The management servers 16A and 16B have functions for the macro cellbase station 10 and the small-to-medium-sized base stations to operatein cooperation with each other. For example, as described above in <3.Control Range A: Central Control of Management Server>, the managementserver 16A receives information (position information, schedulinginformation, Qos information etc.) related to the macro cell basestation 10, the small-to-medium-sized base station, the user equipment20 belonging to the small-to-medium-sized base station or the like,determines the macro cell base station 10 or the small-to-medium-sizedbase station that controls communication interfering with othercommunication, and gives a direction for interference avoidanceoperation. Note that the functions of the management server 16 may beincorporated into the macro cell base station 10 or any one of thesmall-to-medium-sized base stations.

The macro cell base station 10 manages the small-to-medium-sized basestations and the user equipment 20 in the macro cell. For example, asdescribed above in <2-3. Configuration of Base Station>, the macro cellbase station 10 selects a control range allowed to eachsmall-to-medium-sized base station from the control range A, the controlrange B and the control range C. Then, each small-to-medium-sized basestation controls communication with the user equipment 20 in conformitywith the control range selected by the macro cell base station 10.

The hotzone base station 31 (a pico cell base station, a micro cell basestation) has the smaller maximum transmission power than the macro cellbase station 10 and communicates with the macro cell base station 10with use of an interface such as X2 or S1 of a core network. Note thatthe hotzone base station 31 creates OSG (Open Subscriber Group) which isaccessible from any user equipment 20.

The femtocell base station 32 has the smaller maximum transmission powerthan the macro cell base station 10 and communicates with the macro cellbase station 10 with use of a packet exchange network such as ADSL.Alternatively, the femtocell base station 32 may communicate with themacro cell base station 10 by a radio link. Note that the femtocell basestation 32 creates CSG (Closed Subscriber Group) which is accessibleonly from limited user equipment 20.

The RRH cell base station 33 is connected with the macro cell basestation 10 by an optical fiber. Thus, the macro cell base station 10transmits signals to the RRH cell base stations 33A and 33B installed ingeographically different places through the optical fiber and allows theRRH cell base stations 33A and 33B to transmit signals by radio. Forexample, only the RRH cell base stations 33 close to the position of theuser equipment 20 may be used. Note that functions related to a controlsystem are incorporated into the macro cell base station 10, and optimumtransmission mode is selected according to the distribution of the userequipment 20.

FIG. 33 shows the overview of the respective small-to-medium-sized basestations described above. The small-to-medium-sized base stations suchas the hotzone base station 31 and the femtocell base station 32 canautonomously determine interference avoidance control and execute thedetermined interference avoidance control according to the methoddescribed above in <4. Control Ranges B and C: Autonomous Control ofRelay Node>. The interference model and interference avoidance controlin the heterogeneous network are described hereinbelow.

(Interference Model in Heterogeneous Network)

FIG. 34 is an explanatory view showing the interference model in aheterogeneous network. In FIG. 34 and FIGS. 35 to 37 described later,the relay node 30, the hotzone base station 31, the femtocell basestation 32 and so on are not particularly distinguished from oneanother, and they are simply shown as small-to-medium-sized basestations 40.

Referring to FIG. 34, the occurrence of the following interferences isassumed in the heterogeneous network.

(1) Interference between a transmission signal from asmall-to-medium-sized base station 40A and a transmission signal fromthe macro cell base station 10 occurring at a user equipment 20A-2.

(2) Interference between a transmission signal from a user equipment20B-2 and a transmission signal from the macro cell base station 10occurring at a small-to-medium-sized base station 40B.

(3) Interference between a transmission signal from asmall-to-medium-sized base station 40C and a transmission signal fromthe macro cell base station 10 occurring at a small-to-medium-sized basestation 40D.

(4) Interference between a transmission signal from asmall-to-medium-sized base station 40E and a transmission signal from auser equipment 20E-2 occurring at a user equipment 20E-2.

(Interference Avoidance Control in Heterogeneous Network)

Although various kinds of interferences occur in the heterogeneousnetwork as described above, the interferences can be is solved by theinterference avoidance control described above in <3. Control Range A:Central Control of Management Server> or <4. Control Ranges B and C:Autonomous Control of Relay Node>. An example of interference avoidancecontrol is specifically described below.

FIG. 35 is an explanatory view showing an example of interferenceavoidance by handover. In the left part of FIG. 35, a transmissionsignal from the small-to-medium-sized base station 40A and atransmission signal from the macro cell base station 10 interfere at theuser equipment 20A-2. In this case, the interference can be solved bythe handover of the user equipment 20A-2 from the small-to-medium-sizedbase station 40A to a small-to-medium-sized base station 40G withdifferent transmission timing from the macro cell base station 10.

Further, in the left part of FIG. 35, a transmission signal from thesmall-to-medium-sized base station 40E and a transmission signal fromthe user equipment 20E-2 interfere at the user equipment 20E-2. In thiscase, the interference can be solved by the handover of the userequipment 20E-2 from the small-to-medium-sized base station 40E to thesmall-to-medium-sized base station 40F.

The handover between the small-to-medium-sized base stations 40 can bemade according to the handover sequence between the relay nodes 30belonging to the same base station 10 which is described earlier withreference to FIG. 19, for example. Further, the handover between thesmall-to-medium-sized base stations 40 belonging to the different macrocell base stations 10 can be made according to the handover sequencewhich is described earlier with reference to FIG. 20, for example.Although the small-to-medium-sized base station 40 has an interface formaking a direct communication with the management server 16 in somecases, because it is under management of the macro cell base station 10,it performs communication for the handover with the macro cell basestation 10 as shown in FIG. 19 or the like.

However, an interfaces between the macro cell base station 10 and thesmall-to-medium-sized base station 40 differs depending on the type ofthe small-to-medium-sized base station 40. For example, when thesmall-to-medium-sized base station 40 is the hotzone base station 31,the small-to-medium-sized base station 40 and the macro cell basestation 10 perform communication by using the X2 interface. Further,when an interface between the small-to-medium-sized base station 40 andthe macro cell base station 10 is wired, latency may be used as acriterion of judgment of the communication link quality.

FIG. 36 is an explanatory view showing an example of interferenceavoidance by beamforming. In the left part of FIG. 36, a transmissionsignal from the small-to-medium-sized base station 40A and atransmission signal from the macro cell base station 10 interfere at theuser equipment 20A-2. In this case, the interference can be solved bydirecting the reception directivity of the user equipment 20A-2 towardthe direction where the small-to-medium-sized base station 40A isplaced.

Further, in the left part of FIG. 36, a transmission signal from thesmall-to-medium-sized base station 40E and a transmission signal fromthe user equipment 20E-2 interfere at the user equipment 20E-2. In thiscase, the interference can be solved by directing the transmissiondirectivity of the user equipment 20E-2 toward the direction where thesmall-to-medium-sized base station 40F is placed because thetransmission signal from the user equipment 20E-2 thereby does not reachthe user equipment 20E-2.

FIG. 37 is an explanatory view showing an example of interferenceavoidance by transmission power control. In the left part of FIG. 37, atransmission signal from the small-to-medium-sized base station 40A anda transmission signal from the macro cell base station 10 interfere atthe user equipment 20A-2. In this case, if the transmission power of thesmall-to-medium-sized base station 40A is lowered, the user equipment20A-2 is excluded from the radio range of the small-to-medium-sized basestation 40A, and thus the connection between the user equipment 20A-2and the small-to-medium-sized base station 40A is shut down. The userequipment 20A-2 thereby searches for a new connection and makes aconnection to the macro cell base station 10, for example. Therefore,the interference can be solved by lowering the transmission power of thesmall-to-medium-sized base station 40A.

Further, in the left part of FIG. 37, a transmission signal from thesmall-to-medium-sized base station 40E and a transmission signal fromthe user equipment 20E-2 interfere at the user equipment 20E-2. In thiscase, if the transmission power of the small-to-medium-sized basestation 40F is lowered, the user equipment 20E-2 is excluded from theradio range of the small-to-medium-sized base station 40F, and thus theconnection between the user equipment 20E-2 and thesmall-to-medium-sized base station 40F is shut down. The user equipment20E-2 thereby searches for a new connection and makes a connection tothe macro cell base station 10, for example. Therefore, the interferencecan be solved by lowering the transmission power of thesmall-to-medium-sized base station 40F.

<6. Summary>

As described above, according to the embodiment, a control range allowedto the small-to-medium-sized base station such as the relay node 30 canbe selected from a plurality of types of control ranges. Further,according to the embodiment, the management server 16 can achieve thecentral control for avoiding interference between cells formed by therespective base stations 10. Furthermore, according to the embodiment,the small-to-medium-sized base station such as the relay node 30 canautonomously determine interference avoidance control and execute theinterference avoidance control.

Although preferred embodiments of the present invention are described indetail above with reference to the appended drawings, the presentinvention is not limited thereto. It should be understood by thoseskilled in the art that various modifications, combinations,sub-combinations and alterations may occur depending on designrequirements and other factors insofar as they are within the scope ofthe appended claims or the equivalents thereof.

For example, although the case where the control range allowed to therelay node 30 is dynamically selected is described above, the controlrange allowed to the relay node 30 may be fixed. Thus, when the controlrange A is fixedly set to the relay node 30, the interference avoidancecontrol is performed in the procedure described in <3. Control Range A:Central Control of Management Server>. Further, when the control range Bor C is fixedly set to the relay node 30, the interference avoidancecontrol is performed in the procedure described in <4. Control Ranges Band C: Autonomous Control of Relay Node>.

Further, it is not always necessary to execute the respective steps inthe processing of the communication system 1 in this specification inchronological order according to the sequence shown in the sequencecharts. For example, the respective steps in the processing of thecommunication system 1 may be executed in the sequence different fromthe sequence shown in the sequence charts or may be executed inparallel.

Furthermore, it is possible to create a computer program that causeshardware such as a CPU, ROM and RAM incorporated in the base station 10,the management server 16, the relay node 30 or the like to functionequally to the respective elements of the base station 10, themanagement server 16 and the relay node 30 described above. Further, amemory medium that stores such a computer program may be provided.

REFERENCE SIGNS LIST

-   -   10 Base station    -   16 Management server    -   20 User equipment    -   30 Relay node    -   124, 224, 324 Analog processing unit    -   128, 228, 328 AD/DA conversion unit    -   130, 230, 330 Digital processing unit    -   134, 234, 334 Decoder    -   140, 240, 340 Encoder    -   142, 242, 342 Control unit    -   148 Control range selection unit    -   164 Interference determination unit    -   166 Base station management unit    -   232,332 Synchronous unit    -   338 Buffer

The invention claimed is:
 1. An electronic device, comprising: a centralprocessing unit (CPU) configured to: control a first communication witha base station and a second communication with a mobile terminal device;receive resource allocation information from the base station, theresource allocation information including resource information for thesecond communication; and control first communication resources for thesecond communication based on the resource allocation information,wherein the control of the first communication resources includes atleast a first control type or a second control type, wherein the firstcontrol type comprises a first autonomous communication resourcesselection for the second communication based on additional resourcesother than available communication resources indicated in the resourceallocation information, wherein the second control type comprises asecond autonomous communication resources selection, for the secondcommunication, among the available communication resources indicated inthe resource allocation information, wherein one of the first controltype or the second control type is selected for the secondcommunication, based on the available communication resources, whereinthe first control type is selected based on the available communicationresources that are less than a threshold, and wherein the second controltype is selected based on the available communication resources that aregreater than the threshold.
 2. The electronic device according to claim1, wherein the control of the first communication resources furtherincludes a third control type, wherein the third control type operatesto use second communication resources identified by the base station. 3.The electronic device according to claim 1, wherein the resourceallocation information is based on traffic information.
 4. Theelectronic device according to claim 3, wherein the traffic informationindicates a traffic load at the base station.
 5. The electronic deviceaccording to claim 1, wherein the control of the first communicationresources is performed independently.
 6. The electronic device accordingto claim 1, wherein the resource allocation information is based on apower state at the base station.
 7. The electronic device according toclaim 1, wherein the resource allocation information is based on a totalnumber of mobile terminal devices serviced by the base station.
 8. Theelectronic device according to claim 1, wherein the control of the firstcommunication resources is based on whether the electronic device istemporarily installed for an event.
 9. The electronic device accordingto claim 1, wherein the control of the first communication resources isbased on whether the electronic device is located in a coverage area ofthe base station.
 10. A wireless communication method, comprising:controlling a first communication with a base station and a secondcommunication with a mobile terminal device; receiving resourceallocation information from the base station, the resource allocationinformation including resource information for the second communication;and controlling communication resources for the second communicationbased on the resource allocation information, wherein the controlling ofthe communication resources being at least a first control type or asecond control type, wherein the first control type comprising a firstautonomous communication resources selection for the secondcommunication based on additional resources other than availablecommunication resources indicated in the resource allocationinformation, wherein the second control type comprises a secondautonomous communication resources selection, for the secondcommunication, among the available communication resources indicated inthe resource allocation information, wherein one of the first controltype or the second control type is selected for the secondcommunication, based on the available communication resources, whereinthe first control type is selected based on the available communicationresources that are less than a threshold, and wherein the second controltype is selected based on the available communication resources that aregreater than the threshold.
 11. A non-transitory computer-readablemedium having stored thereon computer-executable instructions that, whenexecuted by a processor, cause a computer to perform operations, theoperations comprising: controlling a first communication with a basestation and a second communication with a mobile terminal device;receiving resource allocation information from the base station, theresource allocation information including resource information for thesecond communication; and controlling communication resources for thesecond communication based on the resource allocation information,wherein the controlling of the communication resources being at least afirst control type or a second control type, wherein the first controltype comprising a first autonomous communication resources selection forthe second communication based on additional resources other thanavailable communication resources indicated in the resource allocationinformation, wherein the second control type comprises a secondautonomous communication resources selection, for the secondcommunication, among the available communication resources indicated inthe resource allocation information, wherein one of the first controltype or the second control type is selected for the secondcommunication, based on the available communication resources, whereinthe first control type is selected based on the available communicationresources that are less than a threshold, and wherein the second controltype is selected based on the available communication resources that aregreater than the threshold.